The French patent FR-PS 1 131 825 shows an automatic scale as has been used for many decades in the cereals processing industry for control purposes and for controlling the product flow. It concerns an automatic operation within the framework of the classical weighing technology. A scale pan is filled with product, the weight of the full scale pan is determined after a short settling time, the scale pan is tipped, emptied out and returned to the filling position. The tare weight can be determined at least when weighing for the first time and the weighed bulk product can be calculated. The tare weight is compensated for in many cases, so that the precise weight of every fill can be determined every time in a desired repetition. A determined weight can thus also be preadjusted with corresponding control of metering devices, so that an identical weight, e.g. 50 kg, is delivered with every weighing. This is periodically checked in the case of scales which are subject to weights and measures regulations.
The real disadvantage of this scale system, which is still widespread, consists in that the construction cost is approximately equally high in every case almost regardless of the magnitude of the scale, e.g. in the area of a scale pan content of 5 to 100 kg. Thus, a smaller scale can not be produced very inexpensively. Another disadvantage is the relatively complicated mechanical construction. The cleaning is impeded although there is a particularly large number of locations on the mechanism in which dust can settle. At present, in foodstuffs processing operations, strict demands are placed on hygiene. A complete encasing protects the mechanism from external influences, but creates dead spaces in the interior in which product deposits can remain until the foodstuffs or feedstuffs spoil.
The DDR patent 12 969 shows an automatic scale without housing which comprises a rotatably supported load drum. The weighing receptacle is constructed as a round drum and allows a very rapid rotation. The construction without housing shown in the DDR patent 12 969 would not be suitable for products giving off great quantities of dust, such as flour or feedstuffs components, or additional devices would have to be arranged for keeping the surroundings free of dust.